Micromechanical systems (commonly referred to as “MEMS”) include, for example, microsensors, microactuators, microinstruments, microoptics, and the like. Many MEMS fabrication processes exist, which include silicon lithographic and etching technologies (silicon MEMS) and non-silicon based lithographic technologies such as LIGA as well as other micro-machining processes which all provide a range of part sizes and materials. All these micro-fabrication technologies can be used to directly produce the desired microparts or to produce masters or molds for replication via other processes. Replication is often desirable to provide a faster and more economical production rate.
Unfortunately, there is no currently known way to easily and economically replicate cantilevered multilevel microparts. Such microparts are difficult to replicate as they contain features that overhang recessed areas within the part. When trying to create or use a replication mold for such microparts, the recessed areas may mechanically lock the master or the replicated parts inside the mold. Replication of larger cantilevered designs, as in many commercial injection molded items, often involves the use of specialized molds which can be partially disassembled or split to allow removal of the replicated part or the use of retractable, angled or collapsible cores. These technologies are clearly more difficult to implement in the replication of microscale parts.
Standard micro-fabrication processes and simple plastic replication processes can only fabricate microparts that are essentially extrusions of two-dimensional designs. In other words, current micropart replication techniques produce prismatic microparts. In order to fabricate a cantilevered micropart, prismatic components are often microfabricated separately and then glued or diffusion-bonded together in the proper configuration. U.S. Pat. Nos. 5,735,985 and 5,793,519 to Ghosh et al. disclose the use of poly(dimethylsiloxane) molds to fabricate such prismatic ceramic microparts. In the method of Ghosh et al., however, cantilevered portions must be molded separately and then joined prior to sintering. Such post-fabrication assembly raises the cost of the device considerably.
Other attempts at manufacturing cantilevered multilayered microstructures, such as those discussed in U.S. Pat. No. 5,378,583 to Guckel et al., involve repetitive bonding and exposure of PMMA resist layers in a LIGA process. LIGA involves the deposition of a relatively thick layer of an x-ray resist on a conductive substrate, e.g., metallized silicon, followed by exposure to high-energy x-ray radiation through an x-ray mask, and then removal of the irradiated resist portions using a chemical developer. The mold so provided can be used to prepare structures having horizontal dimensions (i.e., diameters or widths) on the order of micrometers. The PMMA mold with its conducting base is then used to prepare metallic micro-components by electroplating in the cavities (i.e., the developed regions) of the LIGA mold. See, for example, U.S. Pat. Nos. 5,190,637 and 5,576,147 to Guckel et al., and Becker et al. (1986), “Fabrication of microstructures with high aspect ratios and great structural heights by synchrotron radiation lithography, galvanoforming, and plastic molding (LIGA Process),” Microelectronic Engineering 4(1):35–36.
While the methods disclosed by Guckel et al. for forming cantilevered parts are suitable for fabricating individual batches of parts in a repetitive, multi-step process, those methods do not provide for either the fabrication or use of molds which can be used to replicate cantilevered microparts. There exists, therefore, a need for a quick and efficient way to fabricate cantilevered micromolds and to replicate cantilevered microparts, without the need for extensive post-fabrication assembly.